The overall objective of this proposed research is to acquire an understanding of the molecular basis for the recognition of self from non-self invertebrates. The hypothesis to be tested is that invertebrates possess low levels of naturally occurring quasi-specific recognition molecules (receptors) for foreign materials and that the interaction of these receptors with the appropriate foreign determinant results in clearance of the material from the circulation and ultimately in its degradation and externalization. Experiments already conducted indicate that certain crustaceans probably possess such receptors and preliminary efforts with the blue crab have resulted in the purification of proteins that are likely candidates to be these receptors. The major emphasis of the work proposed here will involve experiments designed to prove conclusively that these purified proteins are the receptors participating in in vivo clearance, to develop an in vitro assay for receptor activity and to characterize the structural and functional properties of such receptors. Studies with representatives of other invertebrate phyla will be undertaken to establish the ubiquitousness of these receptors. This proposed research, when completed, may not only offer a "non-immune" explanation for invertebrate immunity but may also lend insight into the evolutionary origins of the hypothetical "primitive" immunoglobulin gene.